Database query processing using a pruning index

ABSTRACT

A source table organized into a set of micro-partitions is accessed by a network-based data warehouse. A pruning index is generated based on the source table. The pruning index comprises a set of filters that indicate locations of distinct values in each column of the source table. A query directed at the source table is received at the network-based data warehouse. The query is processed using the pruning index. The processing of the query comprises pruning the set of micro-partitions of the source table to scan for data matching the query, the pruning of the plurality of micro-partitions comprising identifying, using the pruning index, a sub-set of micro-partitions to scan for the data matching the query.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. Pat. No. 10,942,925, filedJul. 17, 2020, which application is a Continuation of U.S. Pat. No.10,769,150, filed Dec. 26, 2019, the contents of which are incorporatedherein by referenced in their entirety.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to databases and, morespecifically, to generating and using pruning indexes to enhancedatabase query processing in a cloud data warehouse system.

BACKGROUND

Databases are widely used for data storage and access in computingapplications. A goal of database storage is to provide enormous sums ofinformation in an organized manner so that it can be accessed, managed,and updated. In a database, data may be organized into rows, columns,and tables. Databases are used by various entities and companies forstoring information that may need to be accessed or analyzed.

A cloud data warehouse (also referred to as a “network-based datawarehouse” or simply as a “data warehouse”) is a network-based systemused for data analysis and reporting that comprises a central repositoryof integrated data from one or more disparate sources. A cloud datawarehouse can store current and historical data that can be used forcreating analytical reports for an enterprise based on data storedwithin databases of the enterprise. To this end, data warehousestypically provide business intelligence tools, tools to extract,transform, and load data into the repository, and tools to manage andretrieve metadata.

When certain information is to be extracted from a database, a querystatement may be executed against the database data. A cloud datawarehouse system processes the query and returns certain data accordingto one or more query predicates that indicate what information should bereturned by the query. The data warehouse system extracts specific datafrom the database and formats that data into a readable form. However,it can be challenging to execute queries on a very large table because asignificant amount of time and computing resources are required to scanan entire table to identify data that satisfies the query.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure.

FIG. 1 illustrates an example computing environment that includes anetwork-based data warehouse system in communication with a cloudstorage provider system, in accordance with some embodiments of thepresent disclosure.

FIG. 2 is a block diagram illustrating components of a compute servicemanager, in accordance with some embodiments of the present disclosure.

FIG. 3 is a block diagram illustrating components of an executionplatform, in accordance with some embodiments of the present disclosure.

FIG. 4 is a conceptual diagram illustrating generation of a blockedbloom filter, which may form part of a pruning index generated by thenetwork-based data warehouse system based on a source table, inaccordance with some example embodiments.

FIG. 5 illustrates a portion of an example pruning index, in accordancewith some embodiments of the present disclosure.

FIG. 6 illustrates a single bloom filter of a pruning index, inaccordance with some embodiments of the present disclosure.

FIG. 7 is a conceptual diagram illustrating further details regardingthe creation of a pruning index, in accordance with some embodiments.

FIG. 8 is a conceptual diagram illustrating maintenance of a pruningindex, in accordance with some embodiments.

FIGS. 9-13 are flow diagrams illustrating operations of thenetwork-based data warehouse system in performing a method forgenerating and using a pruning index in processing a database query, inaccordance with some embodiments of the present disclosure.

FIG. 14 illustrates a diagrammatic representation of a machine in theform of a computer system within which a set of instructions may beexecuted for causing the machine to perform any one or more of themethodologies discussed herein, in accordance with some embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific example embodiments forcarrying out the inventive subject matter. Examples of these specificembodiments are illustrated in the accompanying drawings, and specificdetails are set forth in the following description in order to provide athorough understanding of the subject matter. It will be understood thatthese examples are not intended to limit the scope of the claims to theillustrated embodiments. On the contrary, they are intended to coversuch alternatives, modifications, and equivalents as may be includedwithin the scope of the disclosure.

As noted above, processing queries directed to very large tables ischallenging because a significant amount of time and computing resourcesare required to scan an entire table to identify data that satisfies thequery. Therefore, it can be desirable to execute a query withoutscanning the entire table. Aspects of the present disclosure address theabove and other challenges in processing queries on large tables bycreating a pruning index that may be used to construct a reduced scanset for processing a query. More specifically, a large source table maybe organized into a set of micro-partitions, and a pruning index can becreated for the source table to be used in identifying a sub-set of themicro-partitions to scan to identify data that satisfies the query.

As discussed herein, a “micro-partition” is a batch unit, and eachmicro-partition has contiguous units of storage. By way of example, eachmicro-partition may contain between 50 MB and 500 MB of uncompresseddata (note that the actual size in storage may be smaller because datamay be stored compressed). Groups of rows in tables may be mapped intoindividual micro-partitions organized in a columnar fashion. This sizeand structure allows for extremely granular selection of themicro-partitions to be scanned, which can be comprised of millions, oreven hundreds of millions, of micro-partitions. This granular selectionprocess for micro-partitions to be scanned is referred to herein as“pruning.” Pruning involves using metadata to determine which portionsof a table, including which micro-partitions or micro-partitiongroupings in the table, are not pertinent to a query, and then avoidingthose non-pertinent micro-partitions when responding to the query, andscanning only the pertinent micro-partitions to respond to the query.Metadata may be automatically gathered about all rows stored in amicro-partition, including: the range of values for each of the columnsin the micro-partition; the number of distinct values; and/or additionalproperties used for both optimization and efficient query processing. Inone embodiment, micro-partitioning may be automatically performed on alltables. For example, tables may be transparently partitioned using theordering that occurs when the data is inserted/loaded. However, itshould be appreciated that this disclosure of the micro-partition isexemplary only and should be considered non-limiting. It should beappreciated that the micro-partition may include other database storagedevices without departing from the scope of the disclosure.

Consistent with some embodiments, a network-based data warehouse systemmay generate a pruning index for a source table and use the pruningindex to prune micro-partitions of the source table when processingqueries directed to the source table. In generating a pruning index, thenetwork-based data warehouse system generates a filter for eachmicro-partition of the source table that indexes distinct values in eachcolumn of the micro-partition of the source table. The filter may, forexample, comprise a blocked bloom filter, a bloom filter, a hash filter,or a cuckoo filter.

When a query comprising an equality predicate is received, rather thanscanning the entire source table to evaluate the equality predicate, thenetwork-based data warehouse system probes the pruning index to identifya reduced scan set of micro-partitions comprising only a sub-set of themicro-partitions of the source table, and only the reduced scan set ofmicro-partitions is scanned when executing the query.

By using a pruning index to prune the set of micro-partitions to scan inexecuting a query, the network-based data warehouse accelerates theexecution of point queries on large tables when compared to conventionalmethodologies. Using a pruning index in this manner also guarantees aconstant overhead for any equality predicate on the table. Additionalbenefits of pruning index utilization in data warehouses include, butare not limited to, an ability to support other types of predicates, anability to quickly compute the number of distinct values in a table, andthe ability to support join pruning.

FIG. 1 illustrates an example computing environment 100 that includes anetwork-based data warehouse system 102 in communication with a storageplatform 104, in accordance with some embodiments of the presentdisclosure. To avoid obscuring the inventive subject matter withunnecessary detail, various functional components that are not germaneto conveying an understanding of the inventive subject matter have beenomitted from FIG. 1. However, a skilled artisan will readily recognizethat various additional functional components may be included as part ofthe computing environment 100 to facilitate additional functionalitythat is not specifically described herein.

As shown, the computing environment 100 comprises the network-based datawarehouse system 102 and a storage platform 104 (e.g., AWS®, MicrosoftAzure Blob Storage®, or Google Cloud Storage®). The network-based datawarehouse system 102 is used for reporting and analysis of integrateddata from one or more disparate sources including storage devices 106-1to 106-N within the storage platform 104. The storage platform 104comprises a plurality of computing machines and provides on-demandcomputer system resources such as data storage and computing power tothe network-based data warehouse system 102.

The network-based data warehouse system 102 comprises a compute servicemanager 108, an execution platform 110, and a database 114. Thenetwork-based data warehouse system 102 hosts and provides datareporting and analysis services to multiple client accounts.Administrative users can create and manage identities (e.g., users,roles, and groups) and use permissions to allow or deny access to theidentities to resources and services.

The compute service manager 108 coordinates and manages operations ofthe network-based data warehouse system 102. The compute service manager108 also performs query optimization and compilation as well as managingclusters of computing services that provide compute resources (alsoreferred to as “virtual warehouses”). The compute service manager 108can support any number of client accounts such as end users providingdata storage and retrieval requests, system administrators managing thesystems and methods described herein, and other components/devices thatinteract with compute service manager 108.

The compute service manager 108 is also in communication with a userdevice 112. The user device 112 corresponds to a user of one of themultiple client accounts supported by the network-based data warehousesystem 102. In some embodiments, the compute service manager 108 doesnot receive any direct communications from the user device 112 and onlyreceives communications concerning jobs from a queue within thenetwork-based data warehouse system 102.

The compute service manager 108 is also coupled to database 114, whichis associated with the data stored in the computing environment 100. Thedatabase 114 stores data pertaining to various functions and aspectsassociated with the network-based data warehouse system 102 and itsusers. In some embodiments, the database 114 includes a summary of datastored in remote data storage systems as well as data available from alocal cache. Additionally, the database 114 may include informationregarding how data is organized in remote data storage systems (e.g.,the storage platform 104) and the local caches. The database 114 allowssystems and services to determine whether a piece of data needs to beaccessed without loading or accessing the actual data from a storagedevice.

For example, the database 114 can include one or more pruning indexes.The compute service manager 108 may generate a pruning index for eachsource table accessed from the storage platform 104 and use a pruningindex to prune the set of micro-partitions of a source table to scan fordata in executing a query. That is, given a query directed at a sourcetable organized into a set of micro-partitions, the computing servicemanger 108 can access a pruning index from the database 114 and use thepruning index to identify a reduced set of micro-partitions to scan inexecuting the query. The set of micro-partitions to scan in executing aquery may be referred to herein as a “scan set.”

in some embodiments, the compute service manager 108 may determine thata job should be performed based on data from the database 114. In suchembodiments, the compute service manager 108 may scan the data anddetermine that a job should be performed to improve data organization ordatabase performance. For example, the compute service manager 108 maydetermine that a new version of a source table has been generated andthe pruning index has not been refreshed to reflect the new version ofthe source table. The database 114 may include a transactional changetracking stream indicating when the new version of the source table wasgenerated and when the pruning index was last refreshed. Based on thattransaction stream, the compute service manager 108 may determine that ajob should be performed. In some embodiments, the compute servicemanager 108 determines that a job should be performed based on a triggerevent and stores the job in a queue until the compute service manager108 is ready to schedule and manage the execution of the job. In anembodiment of the disclosure, the compute service manager 108 determineswhether a table or pruning index needs to be reclustered based on one ormore DML commands being performed, wherein one or more of DML commandsconstitute the trigger event.

The compute service manager 108 is further coupled to the executionplatform 110, which provides multiple computing resources that executevarious data storage and data retrieval tasks. The execution platform110 is coupled to storage platform 104 of the storage platform 104. Thestorage platform 104 comprises multiple data storage devices 106-1 to106-N. In some embodiments, the data storage devices 106-1 to 106-N arecloud-based storage devices located in one or more geographic locations.For example, the data storage devices 106-1 to 106-N may be part of apublic cloud infrastructure or a private cloud infrastructure. The datastorage devices 106-1 to 106-N may be hard disk drives (HDDs), solidstate drives (SSDs), storage clusters, Amazon S3TM storage systems orany other data storage technology. Additionally, the storage platform104 may include distributed file systems (e.g., Hadoop Distributed FileSystems (HDFS)), object storage systems, and the like.

The execution platform 110 comprises a plurality of compute nodes. A setof processes on a compute node executes a query plan compiled by thecompute service manager 108. The set of processes can include: a firstprocess to execute the query plan; a second process to monitor anddelete micro-partition files using a least recently used (LRU) policyand implement an out of memory (OOM) error mitigation process; a thirdprocess that extracts health information from process logs and status tosend back to the compute service manager 108; a fourth process toestablish communication with the compute service manager 108 after asystem boot; and a fifth process to handle all communication with acompute cluster for a given job provided by the compute service manager108 and to communicate information back to the compute service manager108 and other compute nodes of the execution platform 110.

In some embodiments, communication links between elements of thecomputing environment 100 are implemented via one or more datacommunication networks. These data communication networks may utilizeany communication protocol and any type of communication medium. In someembodiments, the data communication networks are a combination of two ormore data communication networks (or sub-networks) coupled to oneanother. In alternate embodiments, these communication links areimplemented using any type of communication medium and any communicationprotocol.

As shown in FIG. 1, the data storage devices 106-1 to 106-N aredecoupled from the computing resources associated with the executionplatform HO. This architecture supports dynamic changes to thenetwork-based data warehouse system 102 based on the changing datastorage/retrieval needs as well as the changing needs of the users andsystems. The support of dynamic changes allows the network-based datawarehouse system 102 to scale quickly in response to changing demands onthe systems and components within the network-based data warehousesystem 102. The decoupling of the computing resources from the datastorage devices supports the storage of large amounts of data withoutrequiring a corresponding large amount of computing resources.Similarly, this decoupling of resources supports a significant increasein the computing resources utilized at a particular time withoutrequiring a corresponding increase in the available data storageresources.

The compute service manager 108, database 114, execution platform 110,and storage platform 104 are shown in FIG. 1 as individual discretecomponents. However, each of the compute service manager 108, database114, execution platform 110, and storage platform 104 may be implementedas a distributed system (e.g., distributed across multiplesystems/platforms at multiple geographic locations). Additionally, eachof the compute service manager 108, database 114, execution platform110, and storage platform 104 can be scaled up or down (independently ofone another) depending on changes to the requests received and thechanging needs of the network-based data warehouse system 102. Thus, inthe described embodiments, the network-based data warehouse system 102is dynamic and supports regular changes to meet the current dataprocessing needs.

During typical operation, the network-based data warehouse system 102processes multiple jobs determined by the compute service manager 108.These jobs are scheduled and managed by the compute service manager 108to determine when and how to execute the job. For example, the computeservice manager 108 may divide the job into multiple discrete tasks andmay determine what data is needed to execute each of the multiplediscrete tasks. The compute service manager 108 may assign each of themultiple discrete tasks to one or more nodes of the execution platform110 to process the task. The compute service manager 108 may determinewhat data is needed to process a task and further determine which nodeswithin the execution platform 110 are best suited to process the task.Some nodes may have already cached the data needed to process the taskand, therefore, be a good candidate for processing the task. Metadatastored in the database 114 assists the compute service manager 108 indetermining which nodes in the execution platform 110 have alreadycached at least a portion of the data needed to process the task. One ormore nodes in the execution platform 110 process the task using datacached by the nodes and, if necessary, data retrieved from the storageplatform 104. It is desirable to retrieve as much data as possible fromcaches within the execution platform 110 because the retrieval speed istypically much faster than retrieving data from the storage platform104.

As shown in FIG. 1, the computing environment 100 separates theexecution platform 110 from the storage platform 104. In thisarrangement, the processing resources and cache resources in theexecution platform 110 operate independently of the data storage devices106-1 to 106-N in the storage platform 104. Thus, the computingresources and cache resources are not restricted to specific datastorage devices 106-1 to 106-N. Instead, all computing resources and allcache resources may retrieve data from, and store data to, any of thedata storage resources in the storage platform 104.

FIG. 2 is a block diagram illustrating components of the compute servicemanager 108, in accordance with some embodiments of the presentdisclosure. As shown in FIG. 2, the compute service manager 108 includesan access manager 202 and a key manager 204 coupled to a data storagedevice 206. Access manager 202 handles authentication and authorizationtasks for the systems described herein. Key manager 204 manages storageand authentication of keys used during authentication and authorizationtasks. For example, access manager 202 and key manager 204 manage thekeys used to access data stored in remote storage devices (e.g., datastorage devices in storage platform 104). As used herein, the remotestorage devices may also be referred to as “persistent storage devices”or “shared storage devices.”

A request processing service 208 manages received data storage requestsand data retrieval requests (e.g., jobs to be performed on databasedata). For example, the request processing service 208 may determine thedata necessary to process a received query (e.g., a data storage requestor data retrieval request). The data may be stored in a cache within theexecution platform 110 or in a data storage device in storage platform104.

A management console service 210 supports access to various systems andprocesses by administrators and other system managers. Additionally, themanagement console service 210 may receive a request to execute a joband monitor the workload on the system.

The compute service manager 108 also includes a job compiler 212, a joboptimizer 214 and a job executor 216. The job compiler 212 parses a jobinto multiple discrete tasks and generates the execution code for eachof the multiple discrete tasks. The job optimizer 214 determines thebest method to execute the multiple discrete tasks based on the datathat needs to be processed. The job optimizer 214 also handles variousdata pruning operations and other data optimization techniques toimprove the speed and efficiency of executing the job. The job executor216 executes the execution code for jobs received from a queue ordetermined by the compute service manager 108.

A job scheduler and coordinator 218 sends received jobs to theappropriate services or systems for compilation, optimization, anddispatch to the execution platform 110. For example, jobs may beprioritized and processed in that prioritized order. In an embodiment,the job scheduler and coordinator 218 determines a priority for internaljobs that are scheduled by the compute service manager 108 with other“outside” jobs such as user queries that may be scheduled by othersystems in the database but may utilize the same processing resources inthe execution platform 110. In some embodiments, the job scheduler andcoordinator 218 identifies or assigns particular nodes in the executionplatform 110 to process particular tasks. A virtual warehouse manager220 manages the operation of multiple virtual warehouses implemented inthe execution platform 110. As discussed below, each virtual warehouseincludes multiple execution nodes that each include a cache and aprocessor.

Additionally, the compute service manager 108 includes a configurationand metadata manager 222, which manages the information related to thedata stored in the remote data storage devices and in the local caches(e.g., the caches in execution platform 110). The configuration andmetadata manager 222 uses the metadata to determine which datamicro-partitions need to be accessed to retrieve data for processing aparticular task or job. A monitor and workload analyzer 224 overseeprocesses performed by the compute service manager 108 and manages thedistribution of tasks (e.g., workload) across the virtual warehouses andexecution nodes in the execution platform 110. The monitor and workloadanalyzer 224 also redistribute tasks, as needed, based on changingworkloads throughout the network-based data warehouse system 102 and mayfurther redistribute tasks based on a user (e.g., “external”) queryworkload that may also be processed by the execution platform 110. Theconfiguration and metadata manager 222 and the monitor and workloadanalyzer 224 are coupled to a data storage device 226. Data storagedevice 226 in FIG. 2 represents any data storage device within thenetwork-based data warehouse system 102. For example, data storagedevice 226 may represent caches in execution platform 110, storagedevices in storage platform 104, or any other storage device.

As shown, the compute service manager 108 further includes a pruningindex generator 228. The pruning index generator 228 is responsible forgenerating pruning indexes to be used in pruning scan sets for queriesdirected to tables stored in the storage platform 104. Each pruningindex comprises a set of filters (e.g., blocked bloom filters, bloomfilters, hash filter, or cuckoo filters) that encode an existence ofunique values in each column of a source table. The pruning indexgenerator 228 generates a filter for each micro-partition of a sourcetable and each filter indicates whether data matching a query ispotentially stored on a particular micro-partition of the source table.Further details regarding the generation of pruning indexes arediscussed below.

FIG. 3 is a block diagram illustrating components of the executionplatform 110, in accordance with some embodiments of the presentdisclosure. As shown in FIG. 3, the execution platform 110 includesmultiple virtual warehouses, including virtual warehouse 1, virtualwarehouse 2, and virtual warehouse n. Each virtual warehouse includesmultiple execution nodes that each includes a data cache and aprocessor. The virtual warehouses can execute multiple tasks in parallelby using the multiple execution nodes. As discussed herein, theexecution platform 110 can add new virtual warehouses and drop existingvirtual warehouses in real-time based on the current processing needs ofthe systems and users. This flexibility allows the execution platform110 to quickly deploy large amounts of computing resources when neededwithout being forced to continue paying for those computing resourceswhen they are no longer needed. All virtual warehouses can access datafrom any data storage device (e.g., any storage device in storageplatform 104).

Although each virtual warehouse shown in FIG. 3 includes three executionnodes, a particular virtual warehouse may include any number ofexecution nodes. Further, the number of execution nodes in a virtualwarehouse is dynamic, such that new execution nodes are created whenadditional demand is present, and existing execution nodes are deletedwhen they are no longer necessary.

Each virtual warehouse is capable of accessing any of the data storagedevices 106-1 to 106-N shown in FIG. 1. Thus, the virtual warehouses arenot necessarily assigned to a specific data storage device 106-1 to106-n and, instead, can access data from any of the data storage devices106-1 to 106-N within the storage platform 104. Similarly, each of theexecution nodes shown in FIG. 3 can access data from any of the datastorage devices 106-1 to 106-N. In some embodiments, a particularvirtual warehouse or a particular execution node may be temporarilyassigned to a specific data storage device, but the virtual warehouse orexecution node may later access data from any other data storage device.

In the example of FIG. 3, virtual warehouse 1 includes three executionnodes 302-1, 302-2, and 302-n. Execution node 302-1 includes a cache304-1 and a processor 306-1. Execution node 302-2 includes a cache 304-2and a processor 306-2. Execution node 302-n includes a cache 304-n and aprocessor 306-n. Each execution node 302-1, 302-2, and 302-n isassociated with processing one or more data storage and/or dataretrieval tasks. For example, a virtual warehouse may handle datastorage and data retrieval tasks associated with an internal service,such as a clustering service, a materialized view refresh service, afile compaction service, a storage procedure service, or a file upgradeservice. In other implementations, a particular virtual warehouse mayhandle data storage and data retrieval tasks associated with aparticular data storage system or a particular category of data.

Similar to virtual warehouse 1 discussed above, virtual warehouse 2includes three execution nodes 312-1, 312-2, and 312-n. Execution node312-1 includes a cache 314-1 and a processor 316-1. Execution node 312-2includes a cache 314-2 and a processor 316-2. Execution node 312-nincludes a cache 314-n and a processor 316-n. Additionally, virtualwarehouse 3 includes three execution nodes 322-1, 322-2, and 322-n.Execution node 322-1 includes a cache 324-1 and a processor 326-1.Execution node 322-2 includes a cache 324-2 and a processor 326-2.Execution node 322-n includes a cache 324-n and a processor 326-n.

In some embodiments, the execution nodes shown in FIG. 3 are statelesswith respect to the data the execution nodes are caching. For example,these execution nodes do not store or otherwise maintain stateinformation about the execution node or the data being cached by aparticular execution node. Thus, in the event of an execution nodefailure, the failed node can be transparently replaced by another node.Since there is no state information associated with the failed executionnode, the new (replacement) execution node can easily replace the failednode without concern for recreating a particular state.

Although the execution nodes shown in FIG. 3 each includes one datacache and one processor, alternate embodiments may include executionnodes containing any number of processors and any number of caches.Additionally, the caches may vary in size among the different executionnodes. The caches shown in FIG. 3 store, in the local execution node,data that was retrieved from one or more data storage devices in storageplatform 104. Thus, the caches reduce or eliminate the bottleneckproblems occurring in platforms that consistently retrieve data fromremote storage systems. Instead of repeatedly accessing data from theremote storage devices, the systems and methods described herein accessdata from the caches in the execution nodes, which is significantlyfaster and avoids the bottleneck problem discussed above. In someembodiments, the caches are implemented using high-speed memory devicesthat provide fast access to the cached data. Each cache can store datafrom any of the storage devices in the storage platform 104.

Further, the cache resources and computing resources may vary betweendifferent execution nodes. For example, one execution node may containsignificant computing resources and minimal cache resources, making theexecution node useful for tasks that require significant computingresources. Another execution node may contain significant cacheresources and minimal computing resources, making this execution nodeuseful for tasks that require caching of large amounts of data. Yetanother execution node may contain cache resources providing fasterinput-output operations, useful for tasks that require fast scanning oflarge amounts of data. In some embodiments, the cache resources andcomputing resources associated with a particular execution node aredetermined when the execution node is created, based on the expectedtasks to be performed by the execution node.

Additionally, the cache resources and computing resources associatedwith a particular execution node may change over time based on changingtasks performed by the execution node. For example, an execution nodemay be assigned more processing resources if the tasks performed by theexecution node become more processor-intensive. Similarly, an executionnode may be assigned more cache resources if the tasks performed by theexecution node require a larger cache capacity.

Although virtual warehouses 1, 2, and n are associated with the sameexecution platform 110, the virtual warehouses may be implemented usingmultiple computing systems at multiple geographic locations. Forexample, virtual warehouse 1 can be implemented by a computing system ata first geographic location, while virtual warehouses 2 and n areimplemented by another computing system at a second geographic location.In some embodiments, these different computing systems are cloud-basedcomputing systems maintained by one or more different entities.

Additionally, each virtual warehouse is shown in FIG. 3 as havingmultiple execution nodes. The multiple execution nodes associated witheach virtual warehouse may be implemented using multiple computingsystems at multiple geographic locations. For example, an instance ofvirtual warehouse 1 implements execution nodes 302-1 and 302-2 on onecomputing platform at a geographic location and implements executionnode 302-n at a different computing platform at another geographiclocation. Selecting particular computing systems to implement anexecution node may depend on various factors, such as the level ofresources needed for a particular execution node (e.g., processingresource requirements and cache requirements), the resources availableat particular computing systems, communication capabilities of networkswithin a geographic location or between geographic locations, and whichcomputing systems are already implementing other execution nodes in thevirtual warehouse.

Execution platform 110 is also fault tolerant. For example, if onevirtual warehouse fails, that virtual warehouse is quickly replaced witha different virtual warehouse at a different geographic location.

A particular execution platform 110 may include any number of virtualwarehouses. Additionally, the number of virtual warehouses in aparticular execution platform is dynamic, such that new virtualwarehouses are created when additional processing and/or cachingresources are needed. Similarly, existing virtual warehouses may bedeleted when the resources associated with the virtual warehouse are nolonger necessary.

In some embodiments, the virtual warehouses may operate on the same datain storage platform 104, but each virtual warehouse has its ownexecution nodes with independent processing and caching resources. Thisconfiguration allows requests on different virtual warehouses to beprocessed independently and with no interference between the requests.This independent processing, combined with the ability to dynamicallyadd and remove virtual warehouses, supports the addition of newprocessing capacity for new users without impacting the performanceobserved by the existing users.

FIG. 4 is a conceptual diagram illustrating generation of a filter 400,which forms part of a pruning index generated by the network-based datawarehouse system 102 based on a source table 402, in accordance withsome example embodiments. As shown, the source table 402 is organizedinto multiple micro-partitions and each micro-partition comprisesmultiple columns in which values are stored.

In generating a pruning index, the compute service manager 108 generatesa filter for each micro-partition of the source table 402, an example ofwhich is illustrated in FIG. 4 as blocked bloom filter 400. Blockedbloom filter 400 comprises multiple bloom filters and encodes theexistence of distinct values in each column of the correspondingmicro-partition. When a query comprising an equality predicate isreceived, rather than scanning the entire source table 402 to evaluatethe equality predicate, the network-based data warehouse system 102probes the pruning index to identify a reduced scan set ofmicro-partitions comprising only a sub-set of the micro-partitions ofthe source table 402.

As shown, the blocked bloom filter 400 is decomposed into N bloomfilters stored as individual columns of the pruning index to leveragecolumnar scans. In generating the blocked bloom filter 400 for aparticular micro-partition of the source table 402, stored values aretransformed into bit positions in the bloom filters. For example, a setof hash values may be generated from stored values in each column of themicro-partition and the set of hash values may be used to set bits inthe bloom filters.

The number of distinct values over all the columns in a micro-partitionis bounded by a maximum size of the micro-partition. As an example, inthe worst case, for a 16 MB partition, the sum of the number of distinctvalues for all columns is at most 4 million (16 MB/4 bytes).Accordingly, to make access of the pruning index as efficient aspossible, each bloom filter 400 is sliced into a fixed number of chunkson the domain of the hash values (e.g., based on the number of distinctvalues per partition), and each bloom filter 400 is further decomposedin a fixed number of M-bit (e.g., 64 bit) values. Each line of theblocked bloom filter 400 is encoded and stored as a single row in thepruning index. Each bloom filter 400 is represented in the pruning indexas a two-dimensional array indexed by the hash values of the storedcolumn values.

FIG. 5 illustrates a portion of an example pruning index 500, inaccordance with some embodiments of the present disclosure. The pruningindex 500 is organized into a plurality of rows and columns. The columnsof the paining index 500 comprise a partition number 502, a slice number504 that provides an encoding of the domain of hash values, a summarytype 506, a hash number 508, and a blocked bloom filter 510 (e.g., theblocked bloom filter 400) that is decomposed into N numeric columns,each column in the blocked bloom filter 510 represents a bloom filter.

Within each row, a micro-partition number or other identifier isincluded in the partition number 502, a slice number is included in theslice number 504 column, an indicator of a summary type is stored in thesummary type 506 column, and a number corresponding to the number ofhash functions used to build the bloom filters is stored in the hashnumber 508 column. Each slice number 504 in the slice number columncomprises a combination of level and block number. The level indicatesthe number of slices of the bloom filter 510 and the block numberindicates the position of the slice in a specific bloom filter 510(e.g., in the bloom filter column). The number of hash functions may betuned to control the false positive rate of the pruning index 500.

The cost in terms of computational resources of accessing a pruningindex is mostly bounded by the size of the index, and thus it isbeneficial to minimize the total size of the pruning index. To this end,the compute service manager 108 can reduce the number of slices computedper micro-partition. The first level of partitioning of the pruningindex is performed to represent the domain of hash values. At oneextreme, a bloom filter can cover the complete domain of hash values(where the bloom filter comprises a single slice) and at the otherextreme a bloom filter can be split in an arbitrary maximum of slices(4096 for example). This decision is parameterized by the number ofdistinct values in the source table because a single slice of thepruning index can only represent a limited number of distinct values.

The number of distinct values significantly impacts the cost ofclustering because it controls the number of rows generated for a givenmicro-partition. For example, a micro-partition with a small number ofdistinct values (e.g., 3) would have a single slice, while amicro-partition with a large number of distinct values (e.g., 1 million)may have the maximum number of slices. In general, the maximum number ofdistinct values determines the maximum number of slices to encode.Accordingly, in some embodiments, the compute service manager 108 uses afirst portion of the hash value (e.g., the 16 higher bits) for the leveland a second portion of the hash value (e.g., the 16 lower bits) foraddressing.

To this end, blocks within the pruning index 500 are organized in ahierarchy that encodes the level of decomposition of the domain ofvalues. As an example of the foregoing, FIG. 6 illustrates a singlebloom filter 600 of a pruning index. In the example illustrated in FIG.6, bloom filter 600 is 2048 bytes and can represent 64 distinct valueswith a false positive rate of 1/1,000,0000. If the correspondingmicro-partition of the source table contains more than 64 distinctvalues, the false positive rate would degrade as soon as the density ofthe bloom filter is larger than ½ (e.g., more bits are set than bits areunset). To address this issue, the compute service manager 108 can, insome embodiments, build two bloom filters (bloom filters 602 and 604),with one bloom filter for each half of the domain.

Each of the bloom filters 602 and 604 will be represented by two rows inthe pruning index, identified by their level and slice number.Consistent with some embodiments, a particular value and itscorresponding hash value maps to a single one of the blocks across allmicro-partitions of the source table. Regardless of the level, a bitencodes a fixed subset of the domain.

Each slice number comprises a combination of a level number and a blocknumber. The level and block number may, in some embodiments, berepresented as two distinct columns, while in other embodiments, alinearization processes is used in clustering to combine these valuestogether to form the slice number.

In some embodiments, the number of hash functions to compute per bloomfilter can be varied to improve performance. This optimization canreduce the CPU cost of building the pruning index while maintaining atarget false positive rate for extremely large tables. Accordingly, insome embodiments, a user may specify a target false positive rate andthe compute service manager 108 may determine the number of hashfunctions to compute per bloom filter as well as the level based on thetarget false positive rate.

FIG. 7 is a conceptual diagram illustrating further details regardingthe creation of a pruning index, in accordance with some embodiments.The creation of a filter (e.g., a blocked bloom filter) is performed bya specialized operator within the compute service manager 108 thatcomputes the set of rows of the pruning index. This operator obtains allthe columns of a particular micro-partition of a source table andpopulates the filter for that micro-partition.

If the total number of distinct values in the source table is unknown,the compute service manager 108 allocates the maximum number of levelsto the pruning index, populates each filter and then applies aconsolidation phase to merge the different filters in a finalrepresentation of the pruning index. The memory allocated to computethis information per micro-partition is constant. In the exampleillustrated in FIG. 7, the memory allocated to compute this informationis a two-dimensional array of 64-bit unsigned integers. The firstdimension is indexed by the level (maximum number of levels) and thesecond dimension is indexed by the number of bloom filters (e.g., 32).Since each partition is processed by a single thread, the total memoryis bounded by the number of threads (e.g., 8) and the maximum level oflevels.

The following snippet of pseudocode represents an example algorithm thatmay be performed by the compute service manager 108 in generating apruning index, consistent with some embodiments.

If it is a new partition:

-   -   Merge all the filters

For each column, do:

-   -   Compute a 32-bits hash value H for each value of the column    -   Compute the level L by using the 16 high bits, L=H>>16    -   Compute the filter at position P=H & (32−1)    -   If the bloom filter does not contain the value,        -   increment the number of distinct values

As shown in FIG. 7, at each partition boundary, the compute servicemanager 108 combines blocks based on a target bloom filter density. Forexample, the compute service manager 108 may combine blocks such thatthe bloom filter density is no more than half. Since the domain ofhashed values is uniform, this can be done incrementally or globallybased on the observed number of distinct values computed above.

If the number of distinct values is known, the compute service manager108 determines the number of levels for the pruning index by dividingthe maximum number of distinct values by the number of distinct valuesper level. To combine two levels, the compute service manager 108performs a logical OR on all the integers representing the filter.

For performance reasons, the filter functions (create and check) combinetwo hash functions (e.g., two 32-bit hash functions). Both the hashfunction computation and the filter derivation needs to be identical onboth the execution platform 110 and compute service manager 108 to allowfor pruning in compute service manager 108 and in the scan setinitialization in the execution platform 110.

FIG. 8 is a conceptual diagram illustrating maintenance of a pruningindex based on changes to a source table, in accordance with someembodiments. As shown, at 800, a change is made to a source table (e.g.,addition of one or more rows or columns). The change to the source tabletriggers generation of additional rows in the pruning index for eachchanged or new micro-partition of the source table, at 802. At a regularinterval, the newly produced rows in the pruning index are reclusteredon the slice number, at 804.

The compute service manager 108 uses a deterministic selection algorithmas part of clustering the prune index. The processing of eachmicro-partition in the source table creates a bounded (and mostlyconstant) number of rows based on the number of distinct values in thesource micro-partition. By construction, those rows are known to beunique and the index domain is non-overlapping for that partition andfully overlapping with already clustered index rows. To minimize thecost of clustering, the compute service manager 108 delays reclusteringof rows until a threshold number of rows have been produced to createconstant partitions.

Although the pruning index is described in some embodiments as beingimplemented specifically with blocked bloom filters, it shall beappreciated that the pruning index is not limited to blocked bloomfilters, and in other embodiments, the pruning index may be implementedusing other filters such as bloom filters, hash filters, or cuckoofilters.

FIGS. 9-13 are flow diagrams illustrating operations of thenetwork-based data warehouse system 102 in performing a method 900 forgenerating and using a pruning index in processing a database query, inaccordance with some embodiments of the present disclosure. The method900 may be embodied in computer-readable instructions for execution byone or more hardware components (e.g., one or more processors) such thatthe operations of the method 900 may be performed by components ofnetwork-based data warehouse system 102. Accordingly, the method 900 isdescribed below, by way of example with reference thereto. However, itshall be appreciated that the method 900 may be deployed on variousother hardware configurations and is not intended to be limited todeployment within the network-based data warehouse system 102.

Depending on the embodiment, an operation of the method 900 may berepeated in different ways or involve intervening operations not shown.Though the operations of the method 900 may be depicted and described ina certain order, the order in which the operations are performed mayvary among embodiments, including performing certain operations inparallel or performing sets of operations in separate processes. Forexample, although the use and generation of the pruning index aredescribed and illustrated together as part of the method 900, it shallbe appreciated that the use and generation of the pruning index may beperformed as separate processes, consistent with some embodiments.

At operation 905, the compute service manager 108 accesses a sourcetable that is organized into a plurality of micro-partitions. The sourcetable comprises a plurality of cells organized into rows and columns anda data value is included in each cell.

At operation 910, the compute service manager 108 generates a pruningindex based on the source table. The pruning index comprises a set offilters (e.g., a set of blocked bloom filters) that index distinctvalues in each column of each micro-partition of the source table. Afilter is generated for each micro-partition in the source table andeach filter is decomposed into N numeric columns (e.g., 32 numericcolumns) to enable integer comparisons. Consistent with someembodiments, the pruning index comprises a plurality of rows and eachrow comprises a micro-partition identifier, a slice number, and a set ofbloom filters.

At operation 915, the compute service manager 108 clusters rows of thepruning index based on slice numbers. In clustering rows based on slicenumbers, the compute service manager 108 groups together rows that havethe same slice number and sorts the row groups in order based oncorresponding slice number.

At operation 920, the compute service manager 108 receives a querydirected at the source table. The query can comprise an equalitypredicate.

At operation 925, the compute service manager 108 accesses the pruningindex associated with the source table based on the query being directedat the source table. For example, the database 114 may store informationdescribing associations between tables and pruning indexes.

At operation 930, the compute service manager 108 works in conjunctionwith the execution platform 110 to process the query using the pruningindex. In processing the query, the compute service manager 108 and/orthe execution platform 110 may use the pruning index to prune the set ofmicro-partitions of the search table to be scanned for data that matchesthe query (e.g., a data value that satisfies the equality predicate).That is, the pruning index may be used to identify a reduced scan setcomprising only a sub-set of the micro-partitions of the source table.The compute service manager 108 uses the pruning index to identify oneor more micro-partitions in which data that satisfies the equalitypredicate is potentially stored. In processing the query, the executionplatform 110 scans the sub-set of micro-partitions of the reduced scanset while foregoing a scan of the remaining micro-partitions.

As shown in FIG. 10, the method 900 may, in some embodiments, furtherinclude operations 1005 and 1010. Consistent with these embodiments, theoperations 1005 and 1010 may be performed as part of the operation 910where the compute service manager 108 generates the pruning index. Theoperations 1005 and 1010 are described below in reference to a singlemicro-partition of the source table simply for ease of explanation.However, it shall be appreciated, that in generating the pruning index,the compute service manager 108 generates a filter for eachmicro-partitions of the source table and thus, the operations 1005 and1010 may be performed for each micro-partition of the source table.

At operation 1005, the compute service manager 108 generates a filterfor a micro-partition of the source table. For example, the computeservice manager 108 may generate a blocked bloom filter for themicro-partition that indexes distinct values in each column of themicro-partition of the source table. Further details regarding thegeneration of the filter for the micro-partition are discussed below inreference to FIG. 11.

At operation 1010, which is optional in some embodiments, the computeservice manager 108 merges one or more rows of the filter. The computeservice manager 122 can merge rows by performing a logical OR operation.The compute service manager 108 may merge rows of the filter until adensity threshold is reached, where the density refers to the ratio of1's and 0's in a row. The density threshold may be based on a targetfalse positive rate.

As shown in FIG. 11, the operation 1005, may, in some embodiments,include operations 1105, 1110, 1115, and 1120. At operation 1105, thecompute service manager 108 computes a number of levels for the filtercorresponding to the micro-partition of the source table. If the numberof distinct values in the micro-partition of the source table isunknown, the compute service manager 108 determines the number of levelsbased on a maximum number of possible distinct values. If the number ofdistinct values in the micro-partition of the source table is known, thecompute service manager 108 determines the number of levels based on thenumber of distinct values.

At operation 1110, the compute service manager 108 identifies a targetcell within the filter based on a given data value included in a columnof a micro-partition of the source table. To identify the target cell,the compute service manager 108 identifies a slice and a filter columnin the filter. The compute service manager 108 identifies the slicebased on the data value and the number of levels in the pruning index.The compute service manager 108 identifies the filter column based onthe data value and a number of filter columns in the blocked bloomfilter.

At operation 1115, the compute service manager 108 generates a hashvalue based on the data value from the source table. In generating thehash value, the compute service manager 108 may apply one or more hashfunctions to the data value. At operation 11120, the compute servicemanager 108 populates the target cell in the blocked bloom filter usingthe hash value.

For ease of explanation, operation 1110, 1115, and 1120 are describedabove in reference to a single data value in a single micro-partition ofthe source table. However, it shall be understood that in generating afilter for a micro-partition of the source table, the operation 1110,1115, and 1120 are repeated for each data value of each column of themicro-partition in the source table.

As shown in FIG. 12, the method 900 may, in some embodiments, includeoperations 1205 and 1210. Consistent with these embodiments, theoperations 1205 and 1210 may be performed as part of operation 925 wherethe compute service manager 108 works in conjunction with the executionplatform 110 to process the query using the pruning index.

At operation 1205, the compute service manager 108 identifies a reducedscan set comprising a sub-set of micro-partitions of the source table toscan for data that satisfies the equality predicate in the query. Thesub-set of micro-partitions of the source table include micro-partitionsdetermined to potentially include the matching data based on the set ofblocked bloom filters in the pruning index. The compute service manager108 may identify the sub-set of micro-partitions by generating a hashvalue based on the equality predicate and identifying one or more valuesin the pruning index that match the hash value. The compute servicemanager 108 identifies one or more micro-partitions that potentiallystore data that satisfies the equality predicate based on the one ormore values in the pruning index that match the hash value. That is, avalue in the pruning index matching the hash value indicates thatmatching data is potentially stored in a micro-partition that can beidentified based on the slice number and filter column corresponding tothe cell of the pruning index in which the value is stored.

The compute service manager 108 communicates the sub-set ofmicro-partitions to the execution platform 110, and the executionplatform 110 scans only the sub-set of micro-partitions of the sourcetable in the reduced scan set to locate data that satisfies the equalitypredicate. In this way, the execution platform 110 searches onlymicro-partitions where matching data is potentially stored whileforegoing an expenditure of additional time and resources to also searchthe remaining micro-partitions for which it is known, based on thepruning index, that matching data is not stored.

Consistent with some embodiments, rather than providing a reduced scanset with micro-partitions of the source table to scan for data, thecompute service manager 108 may instead identify and compile a set ofnon-matching micro-partitions. The compute service manager 108 or theexecution platform 110 may remove micro-partitions from the scan setbased on the set of non-matching micro-partitions.

As shown in FIG. 13, the method 900 may, in some embodiments, includeoperations 1305, 1310, and 1315. Although the operations 1305, 1310, and1315 are illustrated as being performed subsequent to operation 925, itshall be appreciated that the operations 1305, 1310, and 1315 may beperformed at any time subsequent to the operation 910 where computeservice manager 108 generates the pruning index.

At operation 1305, the compute service manager 108 detects a change tothe source table. The change to the source table may include one or morerows being added to and/or deleted from the source table.

At operation 1310, the compute service manager 108 generates one or moreadditional rows in the pruning index associated with the source tablebased on the change to the source table. The compute service manager 108generates additional rows in the same manner in which rows of thepruning index are generated during the initial creation of the pruningindex.

At operation 1315, the compute service manager 108 reclusters thepruning index based on slice number. Consistent with some embodiments,the compute service manager 108 may wait to recluster the pruning indexuntil a threshold number of additional rows have been added to thepruning index.

FIG. 14 illustrates a diagrammatic representation of a machine 1400 inthe form of a computer system within which a set of instructions may beexecuted for causing the machine 1400 to perform any one or more of themethodologies discussed herein, according to an example embodiment.Specifically, FIG. 14 shows a diagrammatic representation of the machine1400 in the example form of a computer system, within which instructions1416 (e.g., software, a program, an application, an applet, an app, orother executable code) for causing the machine 1400 to perform any oneor more of the methodologies discussed herein may be executed. Forexample, the instructions 1416 may cause the machine 1400 to execute anyone or more operations of any one or more of the method 900. As anotherexample, the instructions 1416 may cause the machine 1400 to implementportions of the functionality illustrated in any one or more of FIGS.4-8. In this way, the instructions 1416 transform a general,non-programmed machine into a particular machine 1400 (e.g., the computeservice manager 108, the execution platform 110, and the data storagedevices 206) that is specially configured to carry out any one of thedescribed and illustrated functions in the manner described herein.

In alternative embodiments, the machine 1400 operates as a standalonedevice or may be coupled (e.g., networked) to other machines. In anetworked deployment, the machine 1400 may operate in the capacity of aserver machine or a client machine in a server-client networkenvironment, or as a peer machine in a peer-to-peer (or distributed)network environment. The machine 1400 may comprise, but not be limitedto, a server computer, a client computer, a personal computer (PC), atablet computer, a laptop computer, a netbook, a smart phone, a mobiledevice, a network router, a network switch, a network bridge, or anymachine capable of executing the instructions 1416, sequentially orotherwise, that specify actions to be taken by the machine 1400.Further, while only a single machine 1400 is illustrated, the term“machine” shall also be taken to include a collection of machines 1400that individually or jointly execute the instructions 1416 to performany one or more of the methodologies discussed herein.

The machine 1400 includes processors 1410, memory 1430, and input/output(I/O) components 1450 configured to communicate with each other such asvia a bus 1402. In an example embodiment, the processors 1410 (e.g., acentral processing unit (CPU), a reduced instruction set computing(RISC) processor, a complex instruction set computing (CISC) processor,a graphics processing unit (GPU), a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a radio-frequencyintegrated circuit (RFIC), another processor, or any suitablecombination thereof) may include, for example, a processor 1412 and aprocessor 1414 that may execute the instructions 1416. The term“processor” is intended to include multi-core processors 1410 that maycomprise two or more independent processors (sometimes referred to as“cores”) that may execute instructions 1416 contemporaneously. AlthoughFIG. 14 shows multiple processors 1410, the machine 1400 may include asingle processor with a single core, a single processor with multiplecores (e.g., a multi-core processor), multiple processors with a singlecore, multiple processors with multiple cores, or any combinationthereof.

The memory 1430 may include a main memory 1432, a static memory 1434,and a storage unit 1436, all accessible to the processors 1410 such asvia the bus 1402. The main memory 1432, the static memory 1434, and thestorage unit 1436 store the instructions 1416 embodying any one or moreof the methodologies or functions described herein. The instructions1416 may also reside, completely or partially, within the main memory1432, within the static memory 1434, within the storage unit 1436,within at least one of the processors 1410 (e.g., within the processor'scache memory), or any suitable combination thereof, during executionthereof by the machine 1400.

The I/O components 1450 include components to receive input, provideoutput, produce output, transmit information, exchange information,capture measurements, and so on. The specific I/O components 1450 thatare included in a particular machine 1400 will depend on the type ofmachine. For example, portable machines such as mobile phones willlikely include a touch input device or other such input mechanisms,while a headless server machine will likely not include such a touchinput device. It will be appreciated that the I/O components 1450 mayinclude many other components that are not shown in FIG. 14. The I/Ocomponents 1450 are grouped according to functionality merely forsimplifying the following discussion and the grouping is in no waylimiting. In various example embodiments, the I/O components 1450 mayinclude output components 1452 and input components 1454. The outputcomponents 1452 may include visual components (e.g., a display such as aplasma display panel (PDP), a light emitting diode (LED) display, aliquid crystal display (LCD), a projector, or a cathode ray tube (CRT)),acoustic components (e.g., speakers), other signal generators, and soforth. The input components 1454 may include alphanumeric inputcomponents (e.g., a keyboard, a touch screen configured to receivealphanumeric input, a photo-optical keyboard, or other alphanumericinput components), point-based input components (e.g., a mouse, atouchpad, a trackball, a joystick, a motion sensor, or another pointinginstrument), tactile input components (e.g., a physical button, a touchscreen that provides location and/or force of touches or touch gestures,or other tactile input components), audio input components (e.g., amicrophone), and the like.

Communication may be implemented using a wide variety of technologies.The I/O components 1450 may include communication components 1464operable to couple the machine 1400 to a network 1480 or devices 1470via a coupling 1482 and a coupling 1472, respectively. For example, thecommunication components 1464 may include a network interface componentor another suitable device to interface with the network 1480. Infurther examples, the communication components 1464 may include wiredcommunication components, wireless communication components, cellularcommunication components, and other communication components to providecommunication via other modalities. The devices 1470 may be anothermachine or any of a wide variety of peripheral devices (e.g., aperipheral device coupled via a universal serial bus (USB)). Forexample, as noted above, the machine 1400 may correspond to any one ofthe compute service manager 108, the execution platform 110, and thedevices 1470 may include the data storage device 206 or any othercomputing device described herein as being in communication with thenetwork-based data warehouse system 102 or the storage platform 104.

Executable Instructions and Machine Storage Medium

The various memories (e.g., 1430, 1432, 1434, and/or memory of theprocessor(s) 1410 and/or the storage unit 1436) may store one or moresets of instructions 1416 and data structures (e.g., software) embodyingor utilized by any one or more of the methodologies or functionsdescribed herein. These instructions 1416, when executed by theprocessor(s) 1410, cause various operations to implement the disclosedembodiments.

As used herein, the terms “machine-storage medium,” “device-storagemedium,” and “computer-storage medium” mean the same thing and may beused interchangeably in this disclosure. The terms refer to a single ormultiple storage devices and/or media (e.g., a centralized ordistributed database, and/or associated caches and servers) that storeexecutable instructions and/or data. The terms shall accordingly betaken to include, but not be limited to, solid-state memories, andoptical and magnetic media, including memory internal or external toprocessors. Specific examples of machine-storage media, computer-storagemedia, and/or device-storage media include non-volatile memory,including by way of example semiconductor memory devices, e.g., erasableprogrammable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), field-programmable gate arrays(FPGAs), and flash memory devices; magnetic disks such as internal harddisks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The terms “machine-storage media,” “computer-storage media,” and“device-storage media” specifically exclude carrier waves, modulateddata signals, and other such media, at least some of which are coveredunder the term “signal medium” discussed below.

Transmission Medium

In various example embodiments, one or more portions of the network 980may be an ad hoc network, an intranet, an extranet, a virtual privatenetwork (VPN), a local-area network (LAN), a wireless LAN (WLAN), awide-area network (WAN), a wireless WAN (WWAN), a metropolitan-areanetwork (MAN), the Internet, a portion of the Internet, a portion of thepublic switched telephone network (PSTN), a plain old telephone service(POTS) network, a cellular telephone network, a wireless network, aWi-Fi® network, another type of network, or a combination of two or moresuch networks. For example, the network 1480 or a portion of the network1480 may include a wireless or cellular network, and the coupling 1482may be a Code Division Multiple Access (CDMA) connection, a GlobalSystem for Mobile communications (GSM) connection, or another type ofcellular or wireless coupling. In this example, the coupling 1482 mayimplement any of a variety of types of data transfer technology, such asSingle Carrier Radio Transmission Technology (1×RTT), Evolution-DataOptimized (EVDO) technology, General Packet Radio Service (GPRS)technology, Enhanced Data rates for GSM Evolution (EDGE) technology,third Generation Partnership Project (3GPP) including 3G, fourthgeneration wireless (4G) networks. Universal Mobile TelecommunicationsSystem (UMTS), High-Speed Packet Access (HSPA), WorldwideInteroperability for Microwave Access (WiMAX), Long Term Evolution (LTE)standard, others defined by various standard-setting organizations,other long-range protocols, or other data transfer technology.

The instructions 1416 may be transmitted or received over the network1480 using a transmission medium via a network interface device (e.g., anetwork interface component included in the communication components1464) and utilizing any one of a number of well-known transfer protocols(e.g., hypertext transfer protocol (HTTP)). Similarly, the instructions1416 may be transmitted or received using a transmission medium via thecoupling 1472 (e.g., a peer-to-peer coupling) to the devices 1470. Theterms “transmission medium” and “signal medium” mean the same thing andmay be used interchangeably in this disclosure. The terms “transmissionmedium” and “signal medium” shall be taken to include any intangiblemedium that is capable of storing, encoding, or carrying theinstructions 1416 for execution by the machine 1400, and include digitalor analog communications signals or other intangible media to facilitatecommunication of such software. Hence, the terms “transmission medium”and “signal medium” shall be taken to include any form of modulated datasignal, carrier wave, and so forth. The term “modulated data signal”means a signal that has one or more of its characteristics set orchanged in such a manner as to encode information in the signal.

Computer-Readable Medium

The terms “machine-readable medium,” “computer-readable medium,” and“device-readable medium” mean the same thing and may be usedinterchangeably in this disclosure. The terms are defined to includeboth machine-storage media and transmission media. Thus, the termsinclude both storage devices/media and carrier waves/modulated datasignals.

The various operations of example methods described herein may beperformed, at least partially, by one or more processors that aretemporarily configured (e.g., by software) or permanently configured toperform the relevant operations. Similarly, the methods described hereinmay be at least partially processor-implemented. For example, at leastsome of the operations of the method 900 may be performed by one or moreprocessors. The performance of certain of the operations may bedistributed among the one or more processors, not only residing within asingle machine, but also deployed across a number of machines. In someexample embodiments, the processor or processors may be located in asingle location (e.g., within a home environment, an office environment,or a server farm), while in other embodiments the processors may bedistributed across a number of locations.

Although the embodiments of the present disclosure have been describedwith reference to specific example embodiments, it will be evident thatvarious modifications and changes may be made to these embodimentswithout departing from the broader scope of the inventive subjectmatter. Accordingly, the specification and drawings are to be regardedin an illustrative rather than a restrictive sense. The accompanyingdrawings that form a part hereof show, by way of illustration, and notof limitation, specific embodiments in which the subject matter may bepracticed. The embodiments illustrated are described in sufficientdetail to enable those skilled in the art to practice the teachingsdisclosed herein. Other embodiments may be used and derived therefrom,such that structural and logical substitutions and changes may be madewithout departing from the scope of this disclosure. This DetailedDescription, therefore, is not to be taken in a limiting sense, and thescope of various embodiments is defined only by the appended claims,along with the full range of equivalents to which such claims areentitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent, to those of skill inthe art, upon reviewing the above description.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more,” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended; that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim is still deemed to fall within thescope of that claim.

EXAMPLES

Example 1 is a network-based data warehouse system comprising: at leastone hardware processor; and a memory storing instructions that cause theat least one hardware processor to perform operations comprising:accessing a source table organized into a set of micro-partitions;generating a pruning index based on the source table, the pruning indexcomprising a set of filters that index distinct values in each column ofthe source table; receiving a query directed to the source table; andprocessing the query using the pruning index, the processing of thequery comprising pruning the set of micro-partitions of the source tableto scan for data matching the query, the pruning of the set ofmicro-partitions comprising identifying, using the pruning index, asub-set of micro-partitions to scan for the data matching the query.

In Example 2 the subject matter of Example 1 optionally furthercomprises: generating a filter for each micro-partition of the sourcetable.

In Example 3, the subject matter of any one of Examples 1 and 2optionally further comprises generating a first filter for a firstmicro-partition by performing operations comprising: for a given datavalue, identifying a cell within the first filter based on the datavalue; generating a hash value based on the data value; and populatingthe cell in the first filter using the hash value.

In Example 4; the subject matter of any one of Examples 1-3 optionallyfurther comprises: computing a number of levels in the first filter; andidentifying a slice in the first filter based on the data value and thenumber of levels in the first filter; and identifying a filter columnbased on the data value and a predetermined number of filter columns inthe first bloom blocked filter.

In Example 5; the subject matter of any one of Examples 1-4 optionallyfurther comprises: merging one or more rows of the first filter based ona target false positive rate.

Example 6 comprises the subject matter of any one of Examples 1-5, afilter in the set of filters optionally comprises a set of bloomfilters; and the pruning index optionally comprises a plurality ofcolumns, the plurality of columns comprising a micro-partitionidentifier column, a slice number column, and the set of bloom filters.

In Example 7, the subject matter of any one of Examples 1-6, optionallyfurther comprises: clustering a plurality of rows on a slice numbercolumn.

In Example 8, the filter of any one of Examples 1-7 optionally furthercomprises multiple bloom filters, a number of bloom filters in thefilter being based on a false positive rate constraint.

In Example 9, the subject matter of any one of Examples 1-8 optionallyfurther comprise: generating a hash value based on an equality predicateincluded in the query, identifying one or more values in the pruningindex that match the hash value; and identifying one or moremicro-partitions that potentially satisfy the equality predicate basedon the one or more values in the pruning index that match the hashvalue.

In Example 10, the subject matter of any one of Examples 1-9 optionallyfurther comprises: detecting a change to the source table; generatingone or more additional rows for the pruning index based on the change tothe source table; and recluster pruning index based on slice number.

In Example 11, the subject matter of any one of Examples 1-10 optionallyfurther comprises scanning the sub-set of micro-partitions of the sourcetable to identify data matching the query.

In Example 12, the subject matter of any one of Examples 1-11 optionallyfurther comprises identifying one or more micro-partitions in which datamatching the query is potentially stored.

Example 13 is a method comprising: accessing a source table organizedinto a set of micro-partitions; generating; by one or more hardwareprocessors of a computer, a pruning index based on the source table, thepruning index comprising a set of filters that index distinct values ineach column of the source table; receiving a query directed to thesource table; and processing the query using the pruning index, theprocessing of the query comprising pruning the set of micro-partitionsof the source table to scan for data matching the query, the pruning ofthe set of micro-partitions comprising identifying, using the pruningindex, a sub-set of micro-partitions to scan for the data matching thequery.

In Example 14, the subject matter of Example 13 optionally furthercomprises: generating a filter for each micro-partition of the sourcetable.

In Example 15, the subject matter of any one of Examples 13-14optionally further comprises: generating a first filter for a firstmicro-partition by performing operations comprising: for a given datavalue, identifying a cell within the first filter based on the datavalue; generating a hash value based on the data value; and populatingthe cell in the first filter using the hash value.

In Example 16, the subject matter of any one of Examples 13-15optionally further comprises: computing a number of levels in the firstfilter; and identifying a slice in the first filter based on the datavalue and the number of levels in the first filter; and identifying afilter column based on the data value and a predetermined number offilter columns in the first bloom blocked filter.

In Example 17, the subject matter of any one of Examples 13-16,optionally further comprises: computing a number of levels in thepruning index; identifying a level in the first filter based on the datavalue and the number of levels in the pruning index; and identifying afilter column based on the data value and a predetermined number offilter columns in the first bloom blocked filter.

In Example 18, the subject matter of any one of Examples 13-17optionally further comprises: merging one or more rows of the firstfilter based on a target false positive rate

Example 19 comprises the subject matter of any one of Examples 13-18,wherein a filter in the set of filters optionally comprises a set ofbloom filters; the pruning index further optionally comprises aplurality of columns, the plurality of columns comprising amicro-partition identifier column, a slice number column, and the set ofbloom filters; and the pruning index is optionally clustered on theslice number columns.

In Example 20, the subject matter of any one of Examples 12-19optionally further comprises: generating a hash value based on anequality predicate included in the query; identifying one or more valuesin the pruning index that match the hash value; and identifying one ormore micro-partitions that potentially satisfy the equality predicatebased on the one or more values in the pruning index that match the hashvalue.

In Example 21, the subject matter of any one of Examples 12-20optionally further comprises: detecting a change to the source table;generating one or more additional rows for the pruning index based onthe change to the source table; and reclustering the pruning index basedon slice number.

In Example 22, the subject matter of any one of Examples 12-21optionally further comprises scanning the sub-set of micro-partitions ofthe source table to identify data matching the query.

In Example 23, the subject matter of any one of Examples 12-22optionally further comprises identifying one or more micro-partitions inwhich data matching the query is potentially stored.

Example 24 is computer-storage medium comprising instructions that, whenexecuted by one or more processors of a machine, configure the machineto perform operations comprising: accessing a source table organizedinto a set of micro-partitions; generating a pruning index based on thesource table, the pruning index comprising a set of filters that indexdistinct values in each column of the source table; receiving a querydirected to the source table; and processing the query using the pruningindex, the processing of the query comprising pruning the set ofmicro-partitions of the source table to scan for data matching thequery, the pruning of the set of micro-partitions comprisingidentifying, using the pruning index, a sub-set of micro-partitions toscan for the data matching the query.

In Example 25, the subject matter of Example 24 optionally furthercomprises: generating a filter for each micro-partition of the sourcetable.

In Example 26, the subject matter of any one of Examples 24-25optionally further comprises: generating a first filter for a firstmicro-partition by performing operations comprising: for a given datavalue, identifying a cell within the first filter based on the datavalue; generating a hash value based on the data value; and populatingthe cell in the first filter using the hash value.

In Example 27, the subject matter of any one of Examples 24-26,optionally further comprises: computing a number of levels in the firstfilter; identifying a slice in the first filter based on the data valueand the number of levels in the first filter; and identifying a filtercolumn based on the data value and a number of filter columns in thefirst filter.

Example 28 comprises the subject matter of any one of Examples 24-27,wherein a filter in the set of filters optionally comprises a set ofbloom filters; the pruning index further optionally comprises aplurality of columns, the plurality of columns comprising amicro-partition identifier column, a slice number column, and the set ofbloom filters; and the pruning index is optionally clustered on theslice number columns.

In Example 29, the subject matter of any one of Examples 24-28optionally further comprises: generating a hash value based on anequality predicate included in the query; identifying one or more valuesin the pruning index that match the hash value; and identifying one ormore micro-partitions that potentially satisfy the equality predicatebased on the one or more values in the pruning index that match the hashvalue.

In Example 30, the subject matter of any one of Examples 24-29optionally further comprises: detecting a change to the source table;generating one or more additional rows for the pruning index based onthe change to the source table; and reclustering the pruning index basedon slice number.

The invention claimed is:
 1. A system comprising: at least one hardwareprocessor; and at least one memory storing instructions that cause theat least one hardware processor to perform operations comprising:accessing a source table organized into a set of batch units; generatinga pruning index based on the source table, the pruning index comprisinga set of filters that index distinct values in each column of the sourcetable, the generating of the pruning index comprising generating the setof filters, each filter in the set of filters corresponding to a batchunit in the set of batch units and being represented as an array withmultiple dimensions in the pruning index; and storing, in a database,the pruning index with an association with the source table.
 2. Thesystem of claim 1, wherein the generating of the pruning index comprisesgenerating a first filter for a first batch unit of the set of batchunits in the source table, the first filter indexing distinct values ineach column of the first batch unit.
 3. The system of claim 2, whereinthe generating of the first filter comprises: for a given data value,identifying a cell within the first filter based on the data value;generating a hash value based on the data value; and populating the cellin the first filter using the hash value.
 4. The system of claim 3,wherein the operations further comprise computing a number of levels inthe first filter; wherein the identifying of the cell comprises:identifying a slice in the first filter based on the data value and thenumber of levels in the first filter; and identifying a filter columnbased on the data value and a number of filter columns in the firstfilter.
 5. The system of claim 3, wherein the generating of the firstfilter further comprises: merging one or more rows of the first filterbased on a target false positive rate.
 6. The system of claim 1,wherein: each filter of the set of filters comprises multiple bloomfilters, a number of bloom filters in each filter being based on atarget false positive rate.
 7. The system of claim 1, wherein: eachfilter in the set of filters comprises a set of bloom filters; and thepruning index further comprises a plurality of columns, the plurality ofcolumns comprising a batch unit identifier column, a slice numbercolumn, and the set of bloom filters.
 8. The system of claim 7, furthercomprising: clustering the pruning index based on the slice numbercolumn.
 9. The system of claim 8, wherein the operations furthercomprise: detecting a change to the source table; generating one or moreadditional rows for the pruning index based on the change to the sourcetable; and reclustering the pruning index based on slice numbers. 10.The system of claim 1, wherein the operations further comprise:processing a query using the pruning index, the processing of the querycomprising: identifying, using the pruning index, a sub-set of batchunits to scan for data matching the query; and scanning only the sub-setof batch units of the source table to identify data matching the query.11. The system of claim 10, wherein the processing of the query usingthe pruning index comprises: generating a hash value based on anequality predicate included in the query; identifying one or more valuesin the pruning index that match the hash value; and identifying one ormore batch units that potentially satisfy the equality predicate basedon the one or more values in the pruning index that match the hashvalue.
 12. The system of claim 10, wherein the identifying of thesub-set of batch units to scan for the data matching the query comprisesidentifying one or more batch units in which data matching the query isnot stored.
 13. The system of claim 10, wherein the identifying of thesub-set of batch units to scan for the data matching the query comprisesidentifying one or more batch units in which data matching the query ispotentially stored.
 14. A method comprising: accessing, by one or moreprocessors, a source table organized into a set of batch units;generating, by the one or more processors, a pruning index based on thesource table, the pruning index comprising a set of filters that indexdistinct values in each column of the source table, the generating ofthe pruning index comprising generating the set of filters, each filterin the set of filters corresponding to a batch unit in the set of batchunits and being represented as an array with multiple dimensions in thepruning index; and storing, in a database, the pruning index with anassociation with the source table.
 15. The method of claim 14, whereingenerating of the pruning index comprises generating a first filter fora first batch unit of the set of batch units in the source table, thefirst filter indexing distinct values in each column of the first batchunit.
 16. The method of claim 15, wherein the generating of the firstfilter comprises: for a given data value, identifying a cell within thefirst filter based on the data value; generating a hash value based onthe data value; and populating the cell in the first filter using thehash value.
 17. The method of claim 16, wherein the generating of thefirst filter further comprises: merging one or more rows of the firstfilter based on a target false positive rate.
 18. The method of claim14, wherein: each filter in the set of filters comprises a set of bloomfilters; and the pruning index further comprises a plurality of columns,the plurality of columns comprising a batch unit identifier column, aslice number column, and the set of bloom filters; and the methodfurther comprises clustering the pruning index based on the slice numbercolumn.
 19. The method of claim 18, further comprising: detecting achange to the source table; generating one or more additional rows forthe pruning index based on the change to the source table; andreclustering the pruning index based on slice numbers.
 20. Acomputer-storage medium comprising instructions that, when executed byone or more processors of a machine, configure the machine to performoperations comprising: accessing a source table organized into a set ofbatch units; generating a pruning index based on the source table, thepruning index comprising a set of filters that index distinct values ineach column of the source table, the generating of the pruning indexcomprising generating the set of filters, each filter in the set offilters corresponding to a batch unit in the set of batch units andbeing represented as an array with multiple dimensions in the pruningindex; and storing, in a database, the pruning index with an associationwith the source table.